Characterization of the cryptogein binding sites on plant plasma membranes

Cryptogein is a 98-amino acid proteinaceous elicitor of tobacco defense rea ctions. Specific binding of cryptogein to high affinity binding sites on to bacco plasma membranes has been previously reported (K-d = 2 nM; number of binding sites: 220 fmol/mg of protein). In this study, biochemical characte rization of cryptogein binding sites reveals that they correspond to a plas ma membrane glycoprotein(s) with an N-linked carbohydrate moiety, which is involved in cryptogein binding. Radiation inactivation experiments performe d on tobacco plasma membrane preparations indicated that cryptogein bound s pecifically to a plasma membrane component with an apparent functional mole cular mass of 193 kDa. Moreover, using the homobifunctional cross-linking r eagent disuccinimidyl suberate and tobacco plasma membranes incubated with I-125-cryptogein, we identified, after SDS-polyacrylamide gel electrophores is and autoradiography, two I-125-cryptogein linked N-glycoproteins of abou t 162 and 50 kDa. Similar results were obtained using Arabidopsis thaliana and Acer pseudoplatanus plasma membrane preparations, whereas cryptogein di d not induce any effects on the corresponding cell suspensions. These resul ts suggest that either cryptogein binds to nonfunctional binding sites, hom ologues to those present in tobacco plasma membranes, or that a protein inv olved in signal transduction after cryptogein recognition is absent or inac tive in both A. pseudoplatanus and A. thaliana.